1. Field Of The Invention
Pure water is most commonly produced by distillation which is the oldest and well-known method. In practice, there are currently three different types of distillation systems, namely, standard thermal, multiple effect and vapor compression. All of these types purify by vaporizing a portion of the feed water thereby concentrating impurities in the remaining liquid and subsequently condensing the pure distillate. Often the vapor phase is further purified by filtration or baffling devices that eliminate particles, such as pyrogens, that may be carried over during the vaporization. To maintain the high level of purity, piping and components that are wetted by the vapor or condensate are fabricated from stainless steel or similar non-corrosive materials.
The thermal still is the simplest form. Feed water is passed through a heat exchanger that may be heated by steam or electrical resistance elements. It is brought to boiling and the vapor is then condensed in a second heat exchanger that is usually water cooled. While this is a very simple process there is an inherent and significant lack of efficiency.
Multiple effect stills provide multi-stage variations of the standard still that operate with greater efficiency. For example high pressure steam is used to vaporize feed water in the first stage of such a still. Vapor generated in the first stage is then condensed in a second heat exchanger. Heat released in this phase change is used to vaporize additional feed water. Theoretically given sufficient high steam supply pressure, any number of stages can be so arranged, each producing the same amount of distillate from essentially the same single quantity of latent heat. In practice typical designs incorporate four or five stages. While efficient, multiple effect stills are expensive and require pressure vessels and a reliable supply of high pressure steam.
The vapor compression still utilizes a mechanical compressor to increase the heat energy of the pure water vapor so that the latent heat of condensation can be transferred to the vaporizing feed water through a heat exchanger. Because this latent heat vaporization is recovered, this is a highly efficient system. Further high pressure equipment is not required. On the other hand the mechanical compressor which is most usually constructed from stainless steel is rather expensive and is subject to maintenance problems and contamination problems.
The present invention offers a high level of energy efficiency and yet does not require high pressures, special seals or a mechanical compressor for water vapor compression. The present system incorporates a very high temperature refrigeration circuit to transfer heat release during condensation of the distillate to the feed water.
2. Description Of The Prior Art
Various prior art devices have been utilized to provide high efficiency distillation systems, some utilizing refrigeration or heat pumping systems coordinated therewith such as U.S. Pat. No. 2,619,453 issued Nov. 25, 1952 to R. Andersen on a Vapor-Compression Distillation; U.S. Pat. No. 2,921,004 issued Jan. 12, 1960 to L. Wood on an Apparatus For The Evaporation Or Distillation Of Water; U.S. Pat. No. 3,203,875 issued to H. Sturtevant on Aug. 31, 1965 for an Apparatus For Distilling Water With Waste Heat; U.S. Pat. No. 3,226,306 issued to J. Hausner on Dec. 28, 1965 for a Rotary Film Distillation And Gas Refrigerant Condensing Apparatus; U.S. Pat. No. 3,234,109 issued to E. Lustenader on Feb. 8, 1966 on a Method And Apparatus For Flash Distillation; U.S. Pat. No. 3,299,649 issued to W. McGrath et al on Jan. 24, 1967 for Separation Systems; U.S. Pat. No. 3,404,537 issued to J. Leonard, Jr. on Oct. 8, 1968 for a Combined Refrigeration And Saline Water Conversion System; U.S. Pat. No. 3,461,041 issued to T. Snyder on Aug. 12, 1969 for Vapor Compression Distillation Of Chemically Treated Degassed Saline Water; U.S. Pat. No. 3,461,460 issued to W. McGrath on Aug. 12, 1969 for Flash Distillation With Condensed Refrigerant As Heat Exchanger; U.S. Pat. No. 3,486,985 issued to W. McGrath on Dec. 30, 1969 for Flash Distillation Apparatus With Refrigerant Heat Exchange Circuits; U.S. Pat. No. 3,492,205 issued t. R. Webber on Jan. 27, 1970 for a Distillation System And Method; U.S. Pat. No. 3,522,149 issued to J. Arvan on Jul. 28, 1970 for a Distillation Apparatus To Recover Potable Water From Non-Potable Water; U.S. Pat. No. 4,014,751 issued to J. McCord on Mar. 29, 1977 for a Vapor Generating And Recovering Apparatus; U.S. Pat. No. 4,181,577 issued to N. Foley on Jan. 1, 1980 for a Refrigeration Type Water Desalinization Units; U.S. Pat. No. 4,214,454 issued Jul. 29, 1980 to J. Taylor on a Water Recovery System; U.S. Pat. No. 4,248,056 issued Feb. 3, 1981 to W. Beacham on a Heat Reclaimer For A Heat Pump; U.S. Pat. No. 4,267,022 issued May 12, 1981 to F. Pitcher on an Energy Efficient Process And Apparatus For Desalinizing Water; U.S. Pat. No. 4,278,502 issued to C. Stevens et al on Jul. 14, 1981 for a Chemical Recovery Apparatus; U.S. Pat. No. 4,345,971 issued Aug. 24, 1982 to W. Watson on a Distillation Employing Heat Pump; U.S. Pat. No. 4,390,396 issued to H. Koblenzer on Jun 28, 1983 for an Apparatus For The Distillation of Vaporizable Liquids; U.S. Pat. No. 4,463,575 issued to J. McCord on Aug. 7, 1984 for Vapor Generating And Recovery Apparatus Including A Refrigerant System With Refrigerant Heat Removal Means; U.S. Pat. No. 4,678,587 issued Jul. 7, 1987 to J. Voinche et al on a Water Distillation Method; U.S. Pat. No. 4,770,748 issued to J. Cellini et al on Sep. 13, 1988 for a Vacuum Distillation System and U.S. Pat. No. 4,955,207 issued Sep. 11, 1990 to C. Mink on a Combination Hot Water Heater-Refrigeration Assembly.